A number of recognized processes exist for both the batch and continuous frying of various foods using cooking or frying oils. In each of these processes there is a recognized tendency for the oils which are used to decompose, forming various chemical products therefrom. These chemical products include free fatty acids, along with other impurities and contaminants, including food residue or "crumb" produced during this process itself, along with the products formed by the breakdown of the oils used and the interaction of the oils with food products added thereto. It is also known that in all of these processes the presence of these materials in the cooking oil, as well as the degradation of the oil itself, eventually results in degradation of the frying properties of the oil, until the oil is no longer useful.
A highly successful approach to the problems of the degradation of cooking oils, and the consequent poor cooking products produced thereby, is set forth in U.S. Pat. No. 4,330,564 to Friedman. This patent discloses a fryer oil treatment utilizing expanded rhyolitic material and water, in amounts of from about 33 to 75 wt. % of the composition, for such treatment processes. This material is preferably used in combination with a food-compatible acid, and the particular process to which this patent is directed employs a system in which once treatment is completed the residue of the composition of that invention is removed from the treated oil by means well known in the art for this purpose, i.e. filtering. The oil is thus preferably filtered hot, and with a hand filter or a filter machine, and the cooking process is then permitted to continue. This patent thus discloses that in typical operations used cooking oil can be treated after each frying meal or at the end of each frying day. Filters useful in these inventions are also set forth in this patent, and include as a preferred filter one described in U.S. Pat. No. 4,052,319.
This material has thus become highly significant in a commercial sense in connection with various batch-type processes which are generally used in the retail food industry in areas where used fryer cooking oil is mixed with the composition, including the porous carrier material, and the residue then filtered from the oil. The presence of the water in these compositions results in dispersion of the porous carrier material throughout the hot oil.
The use of these food-compatible acids was previously disclosed in Clewell, Jr. et al, U.S. Pat. No. 3,947,602, disclosing the use of various absorbents, such as diatomaceous earth, activated carbon and the like, to remove contaminants from the used cooking oil, again in a process where filtration is employed in connection with the used oil.
In co-pending U.S. patent application No. 035,071, filed on Apr. 6, 1987, assigned to the assignee of the present application, a continuous treatment process is disclosed in which the oil is continuously recirculated through a cooking zone in the recirculation zone, and the recirculating oil is continuously treated with these treatment compounds, which are capable of selectively reducing the content of surfactants produced from the use of the cooking oil to substantially increase the useful life of the oil in this process. Once again in these processes, as shown in the drawings in this pending patent application, the treatment procedure includes a filtering medium, upon which the treatment material is deposited as it contacts the used oil, and from which it is then removed.
The search has therefore continued for methods for improving the food frying processes, particularly in batch-type operations.